1. Field of the Invention
The present invention relates to a hole punching device, which is used in conjunction with image forming apparatuses, that punch holes in sheets conveyed out from an image forming apparatus such as a copier, printing machine or printer and the like.
2. Description of the Related Arts
Such a variety of hole-punching devices have been well known, as performing punch-holes in sheets by manually pushing hole-punching members downward into a plurality of sheets, and automatic hole-punching devices that punch holes in sheets conveyed out of a printing machine or copies as office devices for punching holes in paper. The former is widely known as a device for penetrating sheets by disposing cylindrically shaped punching members that shuttles up and down, on a frame member that sandwiches sheets. By pressing an operating lever downward, these cylindrically shaped hole-punching members penetrate the sheets thereby punching holes. On the other hand, the latter method uses a drive motor to push punch members through sequentially conveyed out sheets that are set at a predetermined position. These are often incorporated into other devices. Both types of hole-punching devices can simultaneously punch holes in sheets at 2, 3 and 4 positions of predetermined distances. The number of holes and the distances therebetween are set to a uniform standard.
Conventional devices are disclosed in the Japanese Patent Publication Nos. 2001-9791, 2001-26370, 2000-301492, and 2002-36196. These publications disclose disposing an upper frame and a lower frame at a predetermined distance to sandwich sheets set therebetween. The upper frame supports a plurality of hole-punching members to move in up and down directions; the lower frame is formed with die punches (blade-bearing holes) that conform to the hole-punching members. A device is disclosed that uses a drive motor to move a plurality of hole-punch members in a hole-punching direction to punch holes in predetermined position of sheets. Depending on the standard, the plurality of hole-punching members can be selectively operated to punch two, three or four holes. Also, the load torque applied to the drive motor is reduced by delaying the operation of the selected plurality of punch members.
For that reason, each of the plurality of punch members is connected to the drive motor via cam means. The Japanese Pat. Pub. 1 engages a follower pin equipped on each of the punch members with a sliding cam having an upside-down V-shaped cam groove. The sliding cam is supported to move along the upper frame. A drive motor pinion is connected to a gear rack integrally formed on a portion of the sliding cam. Japanese Pat. Pub. 2 discloses connecting an eccentric cam to each hole-punching member composed of the same configuration described above. This eccentric cam is installed on a drive shaft disposed parallel to the upper frame. The drive shaft is connected to a drive motor. The eccentric cam of each punch member selectively punches holes in sheets depending on the rotational angle of the drive shaft. At the same time, a time difference is provided to the operation of the selected plurality of punch members to vary the hole-punching timing.
These Japanese Patent publications disclose a structure where the hole-punching members punch holes in a sheet in the process of moving from a top dead center to a bottom dead center of a thrusting direction, by receiving thrusting force in the hole-punching direction from the V-shaped cam or eccentric cam without rotating around a longitudinal axis of rotation.
When selectively moving the plurality of hole-punching members in the hole-punching direction using cam means as described in the aforementioned Japanese Patent publications, the hole-punching members are moved up and down in the shaft direction by engaging a follower pin integrally formed in the punch members with a sliding cam as described in Japanese Patent Pub. 1. They are also moved up and down by connecting the punch members 40 shaft to an eccentric cam, as described in Japanese Patent Pub. 2. These conventional hole-punching structures have the problems outlined below because hole-punching members are normally formed into a spindle-shape to punch holes in a sheet (or sheet bundle) by a thrusting action that is simply an up and down action.
First, a die having blade-bearing holes is disposed sandwiching the sheets for the punch members that move up and down. A paper cutting debris box is equipped below the die to collect paper cutting debris generated by punching holes in the sheets. In this conventional hole punching device structure wherein punch members move in the up and down direction in only the thrusting direction, paper cutting debris accumulates directly below the blade bearing holes. If the volume of paper cutting debris increases, there is the possibility that the cuttings can find their way into the device through the blade bearing holes. Particularly, when operating the punch and paper cutting debris accumulates into a pile directly below the punch members, a higher load than what is required is applied to the hole-punching members and an excessive load is applied to the drive motor. These loads can lead to mechanical failure. Also, if paper cutting debris on the die gets inside the device, there is the problem of incorrect sensing of the sheet sensor inside the device.
Secondly, with the hole-punching structure that punches holes in sheets using the thrusting action in up and down directions, another load is placed on the drive motor because a high shear strength is required to punch holes in the sheets. For that reason, when punching holes in sheets such as plastic film, or thick sheets, there is a large load placed on the drive motor. This means that the device must either have a large-capacity motor, or a high gear reduction ratio is needed to punch holes at low speed. Therefore, such devices have the particular problems of requiring a large drive unit and higher costs associated with punching holes.